A fuel injector is already known which has a valve needle, that is controlled by an actuator. The actuator is composed, e.g., of an electromagnetic coil or a piezo element. An exemplary fuel injector of the species, having an electromagnetic coil, is described in German Patent No. 35 40 660. The fuel injector has a valve housing, in which a solenoid coil is arranged on a coil support. A valve needle, having a valve closure member that is configured on the former as one piece, cooperates with a valve seat surface forming a sealing seat. At its end facing the solenoid coil, the valve needle is fixedly connected to an armature and is acted upon by a resetting spring against the sealing seat. If a current flows through the solenoid coil, the armature is pulled against the force of the resetting spring and lifts the valve needle off from its sealing seat. The fuel can then exit through a spray-discharge bore hole which adjoins the valve seat.
A disadvantage in this known fuel injector is the fact that the angle at which the injection takes place is fixed, and the quantity of fuel can only be regulated to a very limited degree. It is difficult or impossible to make adjustments with respect to various operating states, such as are necessary in particular in the case of lean- mixture concepts and stratified-charge methods in combination with direct injection into the combustion chamber. For this purpose, it is necessary to attain varying operating states using injection angles that vary in their direction.
German Published Patent Application No. 32 28 079 describes a fuel injector is known which has two valve needles. For converting fuel under medium pressure to fuel under high pressure, the fuel injector has a differential piston. Both valve needles are acted upon by one spring, in each case, against one sealing seat. If the one valve needle is lifted from its sealing seat by the amount of a certain prestroke, then it strikes against a limit stop of the other valve needle and, in the further stroke, it takes this valve needle with it. The two sealing seats of the two valve needles close different spray-discharge openings, which can be oriented at different angles. However, it is not possible to achieve a substantial and individual adjustment with respect to performance characteristics of an internal combustion engine, such as in the case of a fuel injector that is controlled by an actuator. In addition, the design has many parts, and the interposition of a differential piston results in a certain sluggishness of the fuel injector with respect to its response performance.
German Published Patent Application No. 30 48 304 describes a fuel injector for internal combustion engines, having a valve needle and an auxiliary needle in a bore hole of the valve needle. The valve needle, at its segment on the combustion-chamber side configured as a valve closure member, cooperates with a valve seat surface to form a sealing seat, which separates spray-discharge bore holes from a fuel supply. The auxiliary needle, guided in the valve needle, also has a valve closure member, which cooperates with a second valve seat surface of the fuel injector. As a result of a spring placed in the valve needle, the auxiliary needle is pulled against the valve needle, in which direction it also forms a sealing seat along with a valve seat surface in the valve needle. If the hydraulically actuated fuel injector begins to open as a result of an increase in the pressure in the fuel supply line, then the auxiliary needle is pressed from its sealing seat in the valve needle against the sealing seat in the valve body and closes a group of spray-discharge bore holes, while a further group of spray-discharge bore holes is opened. If the pressure continues to increase, then the valve needle is lifted from its sealing seat, and, after a certain stroke, it takes the auxiliary needle with it, the auxiliary needle striking against the limit stop of the valve needle. All spray-discharge bore holes are then released. It is disadvantageous that the driving of the valve needle stroke is only carried out using the pressure of the fuel, and an adjustment with respect to the performance characteristics of an internal combustion engine is therefore only possible to a limited degree.
German Published Patent Application No. 27 11 391 describes a fuel injector having an operating piston for regulating the maximum stroke of a valve needle. The valve needle is acted upon in the closing direction by a spring and cooperates with a valve seat surface to form a sealing seat. The valve needle is controlled purely hydraulically. Using the operating piston, which is also hydraulically adjustable in its stroke, the stroke of the valve needle is limited, or completely prevented. Driving this operating piston is accomplished using its own supply line. In accordance with the stroke of the operating piston, the through-flow quantity of fuel can be limited. It is disadvantageous in the fuel injector that the design is multi-part and cumbersome, and therefore is expensive to manufacture.